Is Spongebob under public domain?

Could you please clarify if the beloved character of Spongebob Squarepants is considered to be under public domain? It's a question that's often raised among fans and creators alike, especially given the longevity and popularity of the show. Is there any legal precedent or information that could help determine the copyright status of this iconic sea sponge? I'm eager to understand the intricacies surrounding the intellectual property rights of such a well-known character.